Introduction
Smart lighting systems combine PIR occupancy sensing with daylight harvesting (adjusting light levels based on available sunlight) to maximize energy savings. This article explains the integration.
What is Daylight Harvesting?
Daylight harvesting automatically dims or turns off electric lights when sufficient natural light is available. A photosensor measures ambient light level and sends this information to the lighting controller.
Combining with PIR Occupancy
The full smart lighting system uses:
- PIR sensor: Detects if space is occupied.
- Photosensor: Measures ambient light level.
- Controller: Makes decisions based on both inputs.
Control Logic
If (occupied) {
If (ambient light < desired level) {
Turn lights ON (or dim to supplement)
} else {
Keep lights OFF (or dim to minimum)
}
} else {
Lights OFF (or very low for safety/security)
}
Integration Options
Separate Sensors
Independent PIR and photosensor connected to a central controller. Flexible but requires more wiring.
Combined Sensor Units
Many manufacturers offer sensors combining PIR and photosensor in a single housing. Examples:
- Leviton OSSMT-GDW: PIR + daylight sensor.
- Lutron LRF2-OCR2B-P: PIR + photosensor.
- Hubbell H-MOSS series: Dual-tech occupancy + daylight.
Sensors with I2C Interface
Digital PIR sensors can be combined with digital light sensors (e.g., TSL2561, BH1750) on the same I2C bus, read by a microcontroller.
Daylight Sensor Placement
- Ceiling-mounted, facing down: Measures light on work plane.
- Near windows: Measures incoming daylight.
- Avoid direct sunlight: Can saturate sensor.
Calibration
The system needs calibration to set:
- Desired light level (setpoint).
- Deadband (to avoid oscillation).
- Fade rates (smooth transitions).
- Minimum dim level.
Energy Savings
Studies show that combining occupancy sensing with daylight harvesting can save 30-60% of lighting energy compared to manual control.
Case Study: Office Retrofit
An office installed PIR/daylight sensors in each cubicle area. Lights automatically turned off when cubicles were empty, and dimmed when sufficient daylight was available. Energy savings: 45%.
Implementation with Arduino/ESP
int pirPin = 2;
int lightSensorPin = A0;
int lightSetpoint = 300; // ADC value
int lightOutput = 9; // PWM to LED
void loop() {
bool occupied = digitalRead(pirPin);
int lightLevel = analogRead(lightSensorPin);
if (occupied) {
if (lightLevel < lightSetpoint) {
int required = map(lightSetpoint - lightLevel, 0, 1023, 0, 255);
analogWrite(lightOutput, required);
} else {
analogWrite(lightOutput, 0);
}
} else {
analogWrite(lightOutput, 0);
}
delay(1000);
}
Conclusion
PIR sensors are essential components of smart lighting systems. Combined with daylight harvesting, they deliver maximum energy efficiency while maintaining occupant comfort.